The conventional dampening unit of this sort is so designed as shown in FIG. 1 in which a dampening roller c which is in rotational contact with a printing plate a and furnishes the printing plate a with dampening water supplied from a water fountain roller b is furnished with ink via an ink accepting roller d from one inking roller f1 of a plurality of inking rollers f1, f2 of an inking unit e, which are in rotational contact with the printing plate a. And, the ink accepting roller d is adapted to come in and out of contact with the inking roller f1 so that with such ink accepting roller d coming in and out of contact, the dampening roller c may furnish the printing plate a with dampening water alone from a water pan g or together with ink from the inking unit e. Shown also in the Figure are a metering roller h in rotational contact with the water fountain roller b and an oscillating roller i in rotational contact with the inking rollers f1, f2 for supplying them with ink.
The modes of furnishing dampening water are changed over in accordance with an image area factor of a print.
To wit, printing as desired requires dampening water to be furnished in the form of a film of uniform thickness onto the printing plate a and to be emulsified (mixed with ink) moderately in the inking unit e. And, such state of emulsification varies with a mode of furnishing water onto the printing plate a and also with an image area factor of a print. Accordingly, if the image area of a print is small, the ink accepting roller d is then spaced from the dampening roller c so that dampening water is directly furnished onto the printing plate a from the dampening roller c. Also, if the print image area is large, then the ink accepting roller d is brought into contact with the dampening roller c so that the dampening roller c furnishes the printing plate a with both water and ink (see JP Patent No. 2882966).
In the conventional dampening unit mentioned above, the ink supply path for a dampening roller is constituted by using only a single roller (ink accepting roller) which is adapted to come into and out of contact with the dampening roller. Thus, ink furnished onto the dampening roller is not fully kneaded in the ink supply path and not fully kneaded either in the water supply path from the dampening roller onto the inking roller. As a result, the problems arise that ink and water on both the dampening roller and the inking roller can hardly be filmed and emulsified and that if the printing plate is furnished with both water and ink as the image area factor becomes larger, then an excessive emulsification goes on to occur quickly so that occurrence of a printing stain soon appears.
With these problems taken into, it is an object of the present invention to provide a dampening unit in an offset printing press in which ink and water are fully kneaded or distributed together when the apparatus is brought into communication with the inking unit and ink can moderately be emulsified on a dampening roller and an inking roller in a mode of furnishing water in which water together with ink is furnished on a printing plate from the inking roller and the dampening roller.